Radio detection and ranging (RADAR) systems can be used to actively estimate parameters of environmental features by emitting radio signals and detecting returning reflected signals. Radar systems can determine the distance to radio-reflective features according to a time delay between transmission and reception. Radar systems can also emit a radio signal that varies in frequency over time, such as a signal with a time-varying frequency ramp or chirp, and then based on the difference in frequency between the emitted signal and the reflected signal estimate range. Some systems may also estimate the relative motion of objects causing radar reflections based on Doppler frequency shifts in the received reflected signals.
A radar system of an airborne platform may be configured to provide information to computational and navigational systems of the airborne platform. The radar system may be able to provide information related to objects that reflect radar signals back to the radar system. The objects that provide radar reflections may be other airborne platforms, ground-based objects, or other objects within the range of the radar system.
Directional antennas can be used for the transmission and/or reception of signals to associate each range estimate with a bearing. More generally, directional antennas can also be used to focus radiated energy on a given field of view of interest. Combining the measured distances and the directional information allows for the surrounding environment features to be mapped.
A navigation system of an airborne platform may be able to determine navigational information of the airborne platform. The navigational information may include both an airspeed and a location of the airborne platform. In many typical situations, location information may be provided through satellite-based location systems, such as the Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), or the Galileo global navigation satellite system (GNSS). Additionally, GPS, GLONASS, and GNSS may be able to provide the airspeed of the airborne platform as well.
In some instances, satellite-based location information may not be available to an airborne platform. For example, a hardware failure or radio jamming may cause satellite-based location information to not be available to the airborne platform. In these instances, it may be desirable to have another system capable of providing location information to the airborne platform. Inertial-based location systems are capable of providing location information based on the movement of the airborne platform from a know reference point. Inertial-based location systems may be known as dead-reckoning based location systems. One shortcoming of inertial-based location systems is the susceptibility to sensor errors, such as sensor drift. For example, if a sensor has a drift (or other error or bias), location information provided by the inertial-based location system may decrease in accuracy as the amount of time the system is used increases. In view of the foregoing, there is a need to develop a system or method that enable a navigation system to correct for sensor errors during the operation of the radar unit.